The present invention generally relates to the field of data buses, and particularly to a data bus for utilization in an avionics environment.
In an avionics environment, data transmission techniques among electronic and computer devices on air transport aircraft typically conform to standards promulgated by Aeronautical Radio, Inc. (ARINC) of Annapolis, Md., such as ARINC 429 or 629. ARINC 429 specifies for unidirectional data flow only, from one transmitting device to one or more receivers. Therefore, a minimum of two buses (one in each direction) is required for two electronic devices to send data to one another, and more may be needed if the data rate cannot be accommodated by the maximum 100 kHz bit rate available on a bus. Adding physical connections (i.e. wires and cabling) negatively affects aircraft cost and weight. However, ARINC 429 is a prolific standard since it is inherently simple in nature, an advantage when safety-analyzing critical avionics systems, and terminal devices are readily available and inexpensive. Although ARINC 629provides a multi-master protocol at 2 MHz bit rates, terminal devices are more complex and much more expensive. Other busing mechanisms being introduced into aircraft have higher complexity, and are not backward compatible to the existing standards (e.g., ARINC 429).
The need for additional avionics bussing capability is also brought about by industry trends toward functional integration, particularly when it is desired to upgrade existing equipment by incorporation of additional functions. While technological advances in processing, memory, etc. may allow much greater functionality to be incorporated into a computer, the existing unit may have limitations in input and output pins as defined by existing aircraft wiring and connector selection, particularly if it is desired to allow the computer to back-fit into an existing aircraft, e.g. for spares commonality. Hence, it is desirable to make the greatest use possible of preexisting pin counts, and one method of doing so is to provide for two-way data transmission on an existing pair of pins previously used only for one-way data transfer.
Thus, there lies a need for a lower cost, relatively non-complex data bus, well-suited to aircraft environmental and certification requirements, with bi-directional or multi-master capability. It would be additionally advantageous for such a bus to be compatible with an existing ARINC standard to the greatest degree possible in order to allow existing test equipment and potentially other existing aircraft equipment to monitor such a bus. This advantage may be increased by providing additional capabilities such as providing increased bit rates over present ARINC standards. Furthermore, the desire to maximize commonality in designs suggests a need for a data bus used to interconnect units in an aircraft to also be useful and efficient for interconnecting modules or assemblies within a unit.
The present invention addresses the need for a simple, low cost, multiple data source databus suitable for an aircraft vehicle or the like for reduced aircraft wiring costs and avionics computer pinout. In addition, it addresses higher speed data bus operation. Combinations of these ideas allows trading off compatibility with existing bus standards and components versus higher bit rates, with the potential of simultaneously accommodating both on a limited basis. Upgrades or retrofits of existing aircraft may particularly benefit from this approach.
Two bus unit improvements are described: multi-source (bi-directional) data transfer capability and higher data rate transfers. A combination of these improvements is also described. Two approaches to multi-source data transfer are described, and two approaches to higher speed operation, along with operation in conjunction with multi-sourcing and intermixture with conventional bit rates.
Therefore, the present invention is directed to an electronic device for communicating via a bus system. In one embodiment, the electronic device includes means for sending and receiving data via a transmission line of the bus system, a transmitter for receiving data from the sending and receiving means and providing the data to the transmission line, a receiver for receiving data from the transmission line and providing the received data to the sending and receiving means, and means for selectively coupling the transmitter to the transmission line according to a protocol of the bus system.
The present invention is further directed to a method for communicating via a bus system. In one embodiment, the method includes steps for coupling a first device to a transmission line whereby the first device may transmit via the transmission line, transmitting data from the first device via the transmission line, upon completion of said transmitting step, transmitting a permission to transmit signal to a second device coupled to the transmission line, decoupling the first device from the transmission line and coupling the second device to the transmission line whereby the second device may transmit via the transmission line, and transmitting data from the second device via the transmission line. In another embodiment, the method includes steps for transmitting data via a transmission line at a first rate by transmitting data from a transmitting device to a receiving device, determining whether to transmit data via the transmission line at a second rate, in the event it is determined to transmit data at a second rate, coupling an impedance to the transmission line whereby a second transmission rate is accommodated, and transmitting data via the transmission line at a the second rate. In an additional embodiment, the method further include steps for, prior to executing the coupling step, determining whether to terminate the transmission line with an appropriate impedance, and, in the event it is determined to terminate the transmission line with an appropriate impedance, executing the coupling step.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.